chore: use less memory when export

[lemmih]

Summary of changes

Changes introduced in this pull request:

• Map directly from Hash to position when compressing .forest.car.zst files.
• Show a progress indicator when exporting snapshots without a forest-node.

The memory required to export a mainnet snapshot goes from 14 GiB to 8 GiB.

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.